The present invention relates to a surgical machine with a sensorless electric motor comprising a rotor and at least two motor windings, and with a motor controller for controlling and/or regulating the electric motor.
The present invention further relates to a method for controlling and/or regulating a surgical machine with a sensorless electric motor comprising a rotor and at least two motor windings, and with a motor controller for controlling and/or regulating the electric motor.
Machines with a power supply which is independent of the mains power supply are being increasingly used in surgery. As a result, converter circuits have to be made available for batteries or accumulators normally used as power supplies, so as to provide time-dependent voltage and current courses required for operating an electric motor with a plurality of, as a rule, three, motor windings, from the DC voltages supplied by the power supplies.
Owing to the power supply being independent of the mains power supply, the electric motor has to be electronically commutated. However, in particular, at low motor rotational speeds, i. e., at rotational speeds of less than 1000 revolutions per minute, increased demands are made on the motor control and/or regulation. Since, in addition, high demands are made on optimum starting behavior of the motor under load and on its dynamics, and, at the same time, the best possible efficiency at each operating point should be achieved, it is necessary to determine the position or location of the rotor of the motor, which is usually formed by a magnet. Only the precise rotor position makes it possible for the coils referred to as motor or stator windings to be supplied with electric current, in accordance with the purpose, at the required point in time of commutation.
It is known to use sensor systems, for example, digital or analog Hall systems, for position recognition. A disadvantage of these configurations is that position sensors have to be integrated into the motor and connected to the motor controller. Consequently, corresponding contacts have to be provided for each position sensor if the motor controller is not fixedly connected to the electric motor. This may result in contact corrosion during cleaning, in particular, sterilization of the machine, and, in the worst case, in the machine being put out of operation.
It is also known to use sensorless rotor position recognition methods for applications where high requirements are not made on the dynamics, the starting torque and the motor quality in the range of low rotational speeds of the motor. Since in conventional electronic commutation methods for electric motors, one motor winding is always not supplied with electric current, the CEMF (counterelectromotive force) is measured at the motor winding that is not supplied with electric current and is evaluated for determining an actual rotational speed of the motor.
The above-described, known controlling and regulating methods for surgical machines either require increased circuitry expenditure and additional components, in particular, sensor systems with position sensors, or are unsuitable for specifically starting the electric motor from a standstill under load and operating the electric motor at very low rotational speeds with a high degree of running smoothness.
The object underlying the present invention is, therefore, to so improve a surgical machine and a method for controlling and regulating a surgical machine of the kind described at the outset that the electric motor is operable with optimum efficiency at low rotational speeds, and a starting of the motor in accordance with the purpose, also under load, is enabled.